Detection method and detection apparatus

ABSTRACT

A detection method of detecting a position of an uppermost substrate of a plurality of substrates stacked on each other includes applying illumination to a region covering a portion of an edge of the uppermost substrate and a portion of a lower substrate stacked with the uppermost substrate, identifying a position of the edge of the uppermost substrate based on a position of a step-like portion present in the region due to a step formed between the uppermost substrate and the lower substrate, and identifying a position of the uppermost substrate based on the position of the edge of the uppermost substrate.

This application is a continuation of Patent Application Serial No.PCT/JP2011/000700, and claims priority to Patent Application Serial No.2010-025935, the contents of each of which are hereby incorporated byreference, in their entirety.

BACKGROUND

1. Technical Field

The present invention relates to a detection method and a detectionapparatus.

2. Related Art

Of a particular interest is a layered semiconductor device in which aplurality of substrates with electronic circuits formed thereon arestacked on each other in order to provide increased mount density forthe semiconductor device. To stack a plurality of substrates on eachother, a substrate bonding apparatus may be used to align and bond thesubstrates (see, for example, Japanese Patent Application PublicationNo. 2009-231671).

To stack a plurality of substrates on each other, the substrates may beappropriately positioned by referring to the outlines of the respectivesubstrates. In this case, the outlines are detected by means of atransmissive optical system. However, when such an optical system isused to detect the outline of a layered substrate having a plurality ofsubstrates stacked on each other and, in particular, the upper substrateis smaller in outline than the lower substrate, it is difficult todetect an accurate outline of the upper substrate.

SUMMARY

Therefore, it is an object of an aspect of the innovations herein toprovide a detection method and a detection apparatus, which are capableof overcoming the above drawbacks accompanying the related art. Theabove and other objects can be achieved by combinations described in theclaims. A first aspect of the innovations may include a detection methodof detecting a position of an uppermost substrate of a plurality ofsubstrates stacked on each other. The detection method includes applyingillumination to a region covering a portion of an edge of the uppermostsubstrate and a portion of a lower substrate stacked with the uppermostsubstrate, identifying a position of the edge of the uppermost substratebased on a position of a step-like portion present in the region due toa step formed between the uppermost substrate and the lower substrate,and identifying a position of the uppermost substrate based on theposition of the edge of the uppermost substrate.

A second aspect of the innovations may include a detection apparatus fordetecting a position of an uppermost substrate of a plurality ofsubstrates stacked on each other. The detection apparatus includes anilluminating section that applies illumination to a region covering aportion of an edge of the uppermost substrate and a portion of a lowersubstrate stacked with the uppermost substrate, and a positionidentifying section that identifies a position of the edge of theuppermost substrate based on a position of a step-like portion presentin the region due to a step formed between the uppermost substrate andthe lower substrate.

The summary clause does not necessarily describe all necessary featuresof the embodiments of the present invention. The present invention mayalso be a sub-combination of the features described above. The above andother features and advantages of the present invention will become moreapparent from the following description of the embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating the structure ofa detection apparatus 100.

FIG. 2 is an explanatory view illustrating an image 106 of a portion ofan edge of a substrate obtained by an image obtaining section.

FIG. 3 illustrates how to identify the position of the portion of theedge of the substrate by means of a position identifying section.

FIG. 4 shows a curve to illustrate how luminance varies at a step-likeportion E.

FIG. 5 is an explanatory view illustrating the detection conditionsunder which the detection apparatus operates.

FIG. 6 is an explanatory view illustrating how to obtain images of threedifferent portions of the edge of the substrate.

FIG. 7 is an explanatory view illustrating how to obtain images whilemoving substrates.

FIG. 8 is an explanatory view illustrating how to obtain images whilemoving substrates.

FIG. 9 is an explanatory view illustrating how to judge the outline andposition of a substrate based on the detected position of the edge ofthe substrate.

FIG. 10 is a front view illustrating an embodiment of scanning incidentlight.

FIG. 11 is a front view illustrating the embodiment of scanning incidentlight.

FIG. 12 is a front view illustrating another embodiment of scanningincident light.

FIG. 13 is an explanatory view illustrating how to obtain images of fourdifferent portions of the edge of the substrate.

FIG. 14 is an explanatory view showing an image of a portion of edges ofsubstrates of a three-layered substrate.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, some embodiments of the present invention will bedescribed. The embodiments does not limit the invention according to theclaims, and all the combinations of the features described in theembodiments are not necessarily essential to means provided by aspectsof the invention.

FIG. 1 is a perspective view schematically illustrating the structure ofa detection apparatus 100 relating to an embodiment. The detectionapparatus 100 is configured to detect the position of an upper substrate104, which is stacked on a lower substrate 102. The detection apparatus100 includes a stage 101, an illuminating section 108, an imageobtaining section 110, and a position identifying section 120.

The lower substrate 102 and the upper substrate 104 are stacked in thethickness direction by means of a substrate bonding apparatus or thelike. The upper substrate 104 is smaller in outline than the lowersubstrate 102. Therefore, at the edge of the upper substrate 104, a stepis formed between the upper surface of the upper substrate 104 and theupper surface of the lower substrate 102.

The stage 101 is configured to have the lower substrate 102 and theupper substrate 104 placed thereon for edge detection. The stage 101 istranslated along the X, Y and Z axes. The stage 101 may be a stage foruse in an apparatus configured to bond another substrate onto the uppersubstrate 104 or the like. In this case, the stage 101 may be configuredto rotate with respect to the X, Y and Z axes. On the upper surface ofthe stage 101, a reference mark 103 is provided. In the perspectiveviews including FIG. 1, the X and Y axes respectively extend in theleft-right direction and back-forth directions within the upper surfaceof the stage 101. The Z axis extends upwards perpendicularly to the Xand Y axes.

The reference mark 103 is used to, for example, adjust the illuminatingsection 108 and the image obtaining section 110. For example, prior tothe task of detecting the position of a substrate, the reference mark103 is used to bring an optical system into a focus to enable an imagecapturing section 105 to form a sharp image of the reference mark 103when a slit image 114 is applied to the reference mark 103. Furthermore,the reference mark 103 is used to associate a position on the stage 101with a position on the image captured by the image capturing section105.

The illuminating section 108 provides the slit image 114 used to detecta position of a substrate. The illuminating section 108 includes a lightsource 119, a lens 118, a slit 116, and a lens 115 in the stated order.

The light source 119 emits light having a wavelength that can bedetected by the image capturing section 105, for example, emits visiblelight when the image capturing section 105 is capable of imaging visiblelight. The lens 118 collects the light from the light source 119. Theslit 116 delimits the illumination used to detect the position of theupper substrate 104. The lens 115 collects the light that has passedthrough the slit 116 to form the slit image 114 on the upper surface ofthe lower substrate 102 and the upper surface of the upper substrate104.

The illuminating section 108 illuminates the lower substrate 102 and theupper substrate 104 at angle with respect to the plane orientation ofthe lower substrate 102 and the upper substrate 104, for example,obliquely downward from top left in FIG. 1. The slit image 114 providedby the illuminating section 108 has, on the lower substrate 102 and theupper substrate 104, an elongated shape extending in the radialdirection of the disk-like lower substrate 102 and the upper substrate104. The area illuminated by the slit image 114 covers a portion of theedge of the upper substrate 104. The illuminating section 108 stores inadvance the position where the edge is expected to be positioned whenthe layered substrate is correctly placed at a predetermined position onthe stage 101 and applies illumination to the expected position. Theedge is a circumference when the lower substrate 102 and the like areshaped as a disk. The edge may have a characteristic such as a notch.

The image obtaining section 110 includes an image capturing section 105and a lens 112. The image obtaining section 110 images a region coveringa portion of the edge of the upper substrate 104 at angle with respectto the plane orientation of the upper substrate 104 and the like,obliquely downward from top right in FIG. 1. In this case, the imageobtaining section 110 also stores in advance the position where the edgeis expected to be positioned when the layered substrate is correctlyplaced at a predetermined position on the stage 101 and images a regioncovering the expected position.

The lens 112 focuses the light reflected from the upper surfaces of thelower substrate 102 and the upper substrate 104 onto the image capturingsection 105. The examples of the image capturing section 105 include aCCD, a CMOS or the like having two-dimensionally arranged pixels. Theimage capturing section 105 produces an image 106 by, on the pixelbasis, converting the optical signals of the image formed on the imagecapturing surface into electrical signals. The position identifyingsection 120 analyzes the image 106 and identifies the position of theedge of the upper substrate 104 based on the position of the step-likeportion present in the image 106.

The optical systems of the illuminating section 108 and the imageobtaining section 110 are not limited to the structures shown in FIG. 1.For example, the lenses 118, 115 and 112 only schematically representthe optical systems and each is not limited to a single lens. Theoptical system of the image obtaining section 110 may be a non-tiltedlens optics or tilted lens optics. If a tilted lens optics is employed,the image obtaining section 110 can focus incoming light within a largeregion on the surfaces of the upper substrate 104 and the lowersubstrate 102 that are at angle with respect to the main light ray bytilting the image capturing section 105.

The following describes a detection method of detecting the position ofthe upper substrate 104 using the detection apparatus 100 shown inFIG. 1. The detection method includes a step of obtaining an image and astep of identifying the position. The step of obtaining an imageincludes a step of applying, by the illuminating section 108,illumination from top left to a region covering a portion of the edge ofthe upper substrate 104 to form the slit image 114, and a step ofimaging, by the image capturing section 105, at angle with respect tothe plane orientation of the lower substrate 102 and the upper substrate104, the slit image 114 reflected by the upper surfaces of the lowersubstrate 102 and the upper substrate 104 to obtain the image 106.

FIG. 2 is an explanatory view illustrating the image 106 of a portion ofthe edge of the substrate obtained by the image obtaining section 110.In the image 106, an upper substrate reflected image 132 corresponds toa portion of the slit image 114 that is reflected by the upper substrate104. On the other hand, a lower substrate reflected image 134corresponds to a portion of the slit image 114 that is reflected by thelower substrate 102.

The step of identifying the position includes a step of forwarding theimage 106 from the image capturing section 105 to the positionidentifying section 120 and a step of performing image analysis by theposition identifying section 120 to identify the position of the edge ofthe upper substrate 104 based on the position of the step-like portion Epresent between the upper substrate reflected image 132 and the lowersubstrate reflected image 134.

The position of the step-like portion E in the image 106 corresponds tothe position of the edge of the upper substrate 104. In FIG. 1, when theedge of the upper substrate 104 is moved toward the back within theregion illuminated by the slit image 114, the position of the step-likeportion E is moved to the left in the image 106. On the other hand, whenthe edge of the upper substrate 104 is moved toward the front in FIG. 1,the position of the step-like portion E is moved to the right in theimage 106. Thus, the position of the edge of the upper substrate 104 canbe identified by analyzing the position of the step-like portion E.

The position identifying section 120 stores thereon in advance thevertical width D of the upper substrate reflected image 132 based on thesize of the slit 116, the optical magnifications of the illuminatingsection 108 and the image obtaining section 110, and the like. Theposition identifying section 120 stores thereon in advance a maximumvalue L_(max) of the horizontal width L of the upper substrate reflectedimage 132 based on the size of the slit 116, the optical magnificationsof the illuminating section 108 and the image obtaining section 110 andthe like.

To analyze the image 106, a selection window 136 is first used to selecta region of the image to be analyzed. In order to identify the upper andlower boundaries of the upper substrate reflected image 132 in the image106, the vertical width b of the selection window 136 is preferablylarger than the width D and the horizontal width a of the selectionwindow 136 is preferably smaller than the width L_(max). Since the uppersubstrate reflected image 132 has higher luminance than the surrounding,the position identifying section 120 can identify the upper and lowerboundaries and the width D of the upper substrate reflected image 132 byanalyzing the vertical luminance variation in the image selected by theselection window 136.

FIG. 3 illustrates how to identify the position of the step-likeportion. In order to identify the position of the step-like portion E,the horizontal width a of the selection window 136 is preferably largerthan the width L_(max), and the vertical width b of the selection window136 is preferably smaller than the width D. The position identifyingsection 120 can identify the position of the step-like portion E byanalyzing the horizontal luminance variation in the image selected bythe selection window 136. The position of the step-like portion E in theimage 106 can be used to identify the position, on the stage 101, theedge of the upper substrate 104 in the region illuminated by the slitimage 114.

FIG. 4 is a curve to illustrate how the luminance varies at thestep-like portion F of the upper substrate reflected image 132 presentin the image 106. In FIG. 4, the horizontal axis represents thehorizontal coordinates in the image 106 shown in FIG. 2 and the like,and the vertical axis represents the luminance. FIG. 4 shows theluminance variation in the upper substrate reflected image 132. Theupper substrate reflected image 132 is ideally expected to exhibit sharpluminance variation at the step-like portion E as indicated by apolygonal line 142. In reality, however, the luminance of the uppersubstrate reflected image 132 gradually varies around the step-likeportion E as shown by a curve 144 due to the aberration of the opticalsystems and the like. Here, the half width Sx of the region in which theluminance gradually varies is referred to as a blurring amount.

The blurring amount Sx caused by the diffraction on the image capturingsurface is on the order of βλ/NA, where β denotes the imagingmagnification ratio of the optical system, λ denotes the wavelength ofthe incident light and NA denotes the numerical aperture of the lens. Toaccurately identify the step-like portion E, three or more measurementsare preferably included within the range of the blurring amount. Forexample, when the image capturing section 105 is formed by using a CCD,three or more pixels are included within the range of Sx under thecondition of (βλ/NA)>3u, where u denotes the size of the pixel of theCCD. In other words, the condition is transformed into NA<(βλ/3u).

For example, when β=1, u=5 μm, and λ=0.67 μm, NA<0.045. This conditionalexpression for NA represents the preferable upper limit for NA when thevariables β, u and λ take the above-mentioned values. When a tilted lensoptics is used, the variable β is replaced with the lateralmagnification β′ of the tilted lens optics.

FIG. 5 is an explanatory view illustrating other conditions. In additionto the blurring amount Sx shown in FIG. 4, there is a blurring amount Syin the vertical direction of the upper substrate reflected image 132 andthe lower substrate reflected image 134. In order to identify thestep-like portion E, the height H of the step-like portion E ispreferably larger than (Sy+mu), where m denotes the number of pixelsused to identify the step-like portion E and thus is an integer of 1 ormore. Considering that the blurring amount Sy is also on the order ofβλ/NA, the following expression is preferably satisfied.H>(βλ/NA)+mu  (1)

The height H of the step-like portion E corresponds to the interval hbetween the upper surface of the lower substrate 102 and the uppersurface of the upper substrate 104, in other words, to the thickness ofthe upper substrate 104. The value of the height H is defined by thefollowing expression.H=2hβ sin θ_(i)  (2)

Here, h denotes the distance between the upper surface of the lowersubstrate 102 and the upper surface of the upper substrate 104, andθ_(i) denotes the incident angle of the incident light. When a tiltedlens optics is used, the variable β is replaced with the lateralmagnification β′ of the tilted lens optics.

When θ_(i) is 90°, sin θ_(i) takes a maximum value of 1. Thus, themaximum value of H can be represented by the following expression.H _(max)=2hβ  (3)

By substituting Expression (3) into Expression (1), the followingexpression is obtained.2hβ>(βλ/NA)+mu  (4)

For example, when β=1, u=5 μm, λ=0.67 μm and m=1, the condition ofNA>0.0012 should be satisfied in order to detect a distance h of 30 μm.This conditional expression for NA represents the preferable lower limitfor NA when the variables β, u, λ and m take the above-mentioned values.

In order to more accurately detect the shape of the upper substrate 104,the incident plane including the incident light and the reflected lightis preferably in contact with the edge of the upper substrate 104. Ifthe incident plane is off the tangential line direction of thesubstrate, the detected results may contain errors. In order to reducesuch errors to fall within the acceptable range, the angle formedbetween the incident plane and the tangential line direction of theupper substrate 104 is preferably adjusted to be 5° or less.

FIG. 6 illustrates another embodiment of how to identify the position ofthe edge of the upper substrate 104. According to this embodiment, theposition of the upper substrate 104 is identified by applying slitimages 114, 172 and 174 to three different portions on the edge of theupper substrate 104 and obtaining images formed by the reflections fromthe respective portions. In this case, detection apparatuses 100corresponding to the slit images 114, 172 and 174 are provided. Each ofthe detection apparatuses 100 can identify the position of the edge of acorresponding one of the portions in accordance with the above-describeddetection method.

In this embodiment, provided that the shape of the upper substrate 104is known in advance, the position of the upper substrate 104 on thestage 101 can be more accurately detected by identifying the positionsof three different portions of the edge of the upper substrate 104 inthe image 106. For example, if the upper substrate 104 is shaped like adisk, the position of the center of the upper substrate 104 and theradius of the upper substrate 104 can be identified by identifying thepositions of three different portions of the edge of the upper substrate104. Thus, the position of the upper substrate 104 can be accuratelydetected. This embodiment can not only achieve highly efficientdetection but also reduce the errors that may occur when a plurality ofportions of a substrate are detected by moving the substrate.

FIGS. 7 and 8 illustrate further different embodiments of identifyingthe position of the edge of the upper substrate 104. FIGS. 7 and 8illustrate operations performed after the operation shown in FIG. 6.According to this embodiment, the upper substrate 104 and the like aremoved relative to the regions to be imaged and the illumination to beapplied to the upper substrate 104 and the like, in order to obtainimages of a plurality of portions and identify a characteristic such asa notch.

In this case, as shown in FIG. 7, the slit image 114 illuminates theregion that includes the notch of the upper substrate 104, the slitimage 172 illuminates the position 90 degrees rotated away from thenotch, and the slit image 174 illuminates the position 180 degreesrotated away from the notch. The slit images 114, 172 and 174 provideelongated illumination extending in the radial direction of the uppersubstrate 104 at their respective positions. Each of the detectionapparatuses 100 obtains an image of a corresponding one of the regionsand identifies the position of a corresponding portion of the edge. Asshown in FIG. 7, the identification of the notch of the upper substrate104 can identify how much the upper substrate 104 has rotated.

In FIGS. 6 to 8, the slit images 114 and 174 longitudinally extend inthe Y axis and the slit image 172 longitudinally extents in the X axis.In this case, the incident plane of the slit image 114 or 174 isvertical to the Y axis. The incident plane of the slit image 172 isvertical to the X axis.

In FIGS. 7 and 8, the stage 101 is moved in the X direction, or to theright in FIGS. 7 and 8, from the position of the upper substrate 104 andthe like shown in FIG. 6, as a result of which the upper substrate 104and the lower substrate 102 are moved and a plurality of differentportions of the edge are thus detected. In this case, the imageobtaining section 110 captures a plurality of images 106, while theilluminating section 108 and the image obtaining section 110 remainsstationary and the stage 101 is moved at a constant rate. Here, thestage 101 may be moved intermittently and the images 106 may be obtainedwhile the stage 101 is temporarily stationary.

FIG. 9 illustrates, as an example, the information about the pluralityof different portions of the edge that is obtained by the embodimentshown in FIGS. 6 to 8. FIG. 9 shows the position (Y1, Y2, . . . ) of thestep-like portion in the image 106 corresponding to the slit image 114in FIGS. 6 to 8 and the associated position (X1, X2, . . . ) on the Xaxis of the stage 101. Based on the shown information, the position ofthe notch on the stage 101 can be identified in the X and Y axes.

The method in which a plurality of portions of the edge are identifiedby moving the upper substrate 104 and the like is not limited to thecase shown in FIGS. 6 to 8 where three slit images are applied to thelayered substrate, in other words, the case where the three detectionapparatuses 100 are used to identify three different points on thelayered substrate. This method is applicable to a case where a singlepoint is identified as shown in FIG. 1, and to a case where more or lessthan three points are identified. In the case where a single point isidentified, the position and shape of the upper substrate 104 can bedetected by moving the upper substrate 104 and the like to identify aplurality of portions of the edge.

When the stage 101 is moved, vibration and the like may occur and changethe relative positions of the stage 101 and the image capturing section105 during the movement. This may lead to erroneously identifiedpositions. When a plurality of portions are identified as shown in FIGS.6 to 8, on the other hand, the detection apparatuses 100 associated withthe slit images 114 and 174 detect the variation in position resultingfrom the vibration in the Y axis. The detected variation in positionresulting from the vibration in the Y axis is used to correct the valuein the Y axis included in the position information identified by usingthe slit image 172. Similarly, the detection apparatus 100 associatedwith the slit image 172 detects the variation in position resulting fromthe vibration in the X axis. The detected variation in positionresulting from the vibration in the X axis is used to correct the valuein the X axis included in the position information identified by usingthe slit images 114 and 174. Such correction enables the shape andposition of the upper substrate 104 to be more accurately detected.

FIGS. 10 and 11 are front views to illustrate an embodiment of scanningthe illumination. According to the embodiment shown in FIGS. 10 and 11,a plurality of portions of the edge are detected by moving theillumination to illuminate different regions, instead of moving thestage 101.

As shown in FIG. 10, the illuminating section 108 has a parallel plateglass 182 on the side of the image with respect to the lens 115, inother words, between the lens 115 and the layered substrate. Since theentrance surface of the parallel plate glass 182 is oriented vertical tothe principal light ray in FIG. 10, the illumination is applied to theposition x₁ after transmitting through the parallel plate glass 182.Here, the position x₁ is on the extended line from the center of thelens in the direction of the principal light ray.

As shown in FIG. 11, if the parallel plate glass 182 is tilted at anglewith respect to the principal light ray through the lens, the positionto which the illumination is applied can be moved from x₁ to x₂ withoutchanging the angle at which the illumination is incident on the layeredsubstrate. In this way, a plurality of portions of the edge can bedetected by changing the angle of the parallel plate glass 182 to scanthe layered substrate with the illumination.

FIG. 12 is a front view illustrating another embodiment of scanning theillumination. In FIG. 12, the illuminating section 108 has a mirror 184at the position of the pupil. The slit image 114 can be applied todifferent positions by changing the angle of the mirror 184.

According to the embodiments shown in FIGS. 10 to 12, it is notnecessary to move the stage 101 having the layered substrate placedthereon. As a result, the detection apparatus 100 as a whole can be mademore compact.

In order to more accurately detect the shape of the upper substrate 104,the incident plane including the incident light and the reflected lightis preferably in contact with the edge of the upper substrate 104. Ifthe stage 101 or incident light is moved within a large area, a largeangle may be formed between the edge and the incident plane within thedetectable region, in which case the detected result may be lessaccurate (see FIGS. 6 to 8). Therefore, if the measurement is performedwhile the stage 101 or incident light is moved, it is preferable tolimit the movable range of the stage 101 or incident light. For example,when the slit 116 having a width of 0.065 mm is used to detect the edgeof the upper substrate 104 having a size of approximately 300 mm, theupper substrate 104 is pre-aligned in such a manner that the notch isoriented in the Y direction with respect to the center of the substrateand then arranged on the stage 101, and the edge of the upper substrate104 may be accurately detected while the stage 101 or incident light ismoved within 5 mm or less.

FIG. 13 illustrates an embodiment of identifying four differentportions. In addition to the slit images 114, 172 and 174 shown in FIG.6, a slit image 188 is additionally provided that is applied to theposition 180 degrees rotated away from the slit image 172. In this way,four different portions of the edge can be identified simultaneously. Inthis case, if one of the four slit images is applied to the position ofthe notch of the upper substrate 104, the other three slit images can beused to simultaneously detect the position of the center of the uppersubstrate 104.

FIG. 14 is an explanatory view showing an image of a portion of edges ofsubstrates that can be obtained by means of the detection apparatus 100shown in FIG. 1 when three substrates with different sizes are stackedon each other. For example, when a substrate larger than the lowersubstrate 102 is placed under the lower substrate 102 in FIG. 1, thethree substrates produce, in the image 106, the upper substratereflected image 132, the lower substrate reflected image 134 and athree-layered substrate reflected image 192 from the above. In thiscase, the above-described method can be used to detect the position ofthe edge of the uppermost upper substrate 104 as long as a sufficientlydistinguishable step-like portion E is present in association with theedge of the upper substrate 104 in the upper substrate reflected image132.

As is apparent from the above, the present embodiment enables anapparatus configured to manufacture a layered semiconductor apparatus bybonding a plurality of substrates together to accurately detect theoutlines and positions of the substrates to be bonded together. In thisway, the substrates to be bonded together can be accurately aligned witheach other.

In the above-described embodiment, the image obtaining section 110 ispositioned to obtain an image formed by the specular reflection of theillumination applied at angle by the illuminating section 108. However,the arrangement of the illuminating section 108 and the image obtainingsection 110 is not limited to such. As an alternative example, theilluminating section 108 may be at angle with respect to the plane ofthe substrate, and the image obtaining section 110 may obtain an imagein the normal direction of the plane orientation of the substrate. As afurther alternative example, the illuminating section 108 may apply theillumination in the normal direction to the plane of the substrate, andthe image obtaining section 110 may obtain an image at angle withrespect to the plane orientation of the substrate. As a yet furtheralternative example, the illuminating section 108 and the imageobtaining section 110 may be both positioned at angle with respect tothe plane of the substrate and off the specular reflection.

In the above-described embodiment, the slit image 114 is used as theillumination. However, the examples of the illumination are not limitedto such. As an alternative, the negative-positive relation between theslit image 114 and the surrounding may be reversed. In other words, theillumination may be designed to have a slit-like shade surrounded bylight. In this case, the illumination is preferably patterned to extendin the radial direction of the substrate when the substrate is circular.

While the embodiments of the present invention have been described, thetechnical scope of the invention is not limited to the above describedembodiments. It is apparent to persons skilled in the art that variousalterations and improvements can be added to the above-describedembodiments. It is also apparent from the scope of the claims that theembodiments added with such alterations or improvements can be includedin the technical scope of the invention.

The operations, procedures, steps, and stages of each process performedby an apparatus, system, program, and method shown in the claims,embodiments, or diagrams can be performed in any order as long as theorder is not indicated by “prior to,” “before,” or the like and as longas the output from a previous process is not used in a later process.Even if the process flow is described using phrases such as “first” or“next” in the claims, embodiments, or diagrams, it does not necessarilymean that the process must be performed in this order.

What is claimed is:
 1. A method comprising: applying illumination to aregion covering a portion of an edge of an uppermost substrate and aportion of a lower substrate stacked with the uppermost substrate;identifying a position of the edge of the uppermost substrate based on aposition of a step-like portion present in the region due to a stepformed between the uppermost substrate and the lower substrate; andidentifying a position of the uppermost substrate based on the positionof the edge of the uppermost substrate; wherein at least one of theapplication of illumination and the position identification is performedat an obliquely downward angle with respect to a plane orientation ofthe lower substrate.
 2. The method as set forth in claim 1, furthercomprising obtaining at least one of an upper reflection image formed byreflection from the uppermost substrate and a lower reflection imageformed by reflection from the lower substrate, wherein in theidentifying the position of the edge of the uppermost substrate, thestep-like portion is identified based on one of the upper reflectionimage and the lower reflection image.
 3. The method as set forth inclaim 2, wherein the identifying the position of the edge of theuppermost substrate includes detecting the step-like portion based on adifference in luminance between the upper reflection image and the lowerreflection image.
 4. The method as set forth in claim 2, wherein theobtaining includes obtaining an image formed by specular reflection fromthe region to which the illumination is applied in the applying.
 5. Themethod as set forth in claim 2, further comprising moving the pluralityof substrates in a direction intersecting a radial direction of theuppermost substrate, when the uppermost substrate is circular, whereinthe obtaining includes obtaining images of the region, at a plurality ofpositions of the uppermost substrate that are created by the movement ofthe substrates, and the identifying the position of the uppermostsubstrate includes detecting a position of a characteristic included inthe edge based on the position of the step-like portion in the imagesobtained at the plurality of positions of the uppermost substrate. 6.The method as set forth in claim 2, wherein when the edge of theuppermost substrate includes a notch, the obtaining includes imaging aplurality of regions of the uppermost substrate, and the identifying theposition of the uppermost substrate includes identifying a rotatingdirection of the notch based on one of the plurality of regionsincluding the notch.
 7. The detection method as set forth in claim 6,further comprising moving the plurality of substrates in a directionintersecting the radial direction, wherein the obtaining includesobtaining images of the one of the plurality of regions including thenotch at a plurality of positions of the uppermost substrate created bythe movement of the substrates, and the identifying the position of theedge includes detecting a position of a characteristic included in thenotch based on the position of the step-like portion of the imagesobtained at the plurality of positions of the uppermost substrate. 8.The method as set forth in claim 7, comprising correcting the positionof the characteristic included in the notch, based on a variation in theposition of the edge among the images of the plurality of regions thatare obtained at the plurality of positions which do not include thenotch.
 9. The method as set forth in claim 6, wherein the applyingincludes scanning the illumination in a direction intersecting theradial direction, and the identifying the position of the uppermostsubstrate includes identifying a position of a characteristic includedin the notch based on the position of the step-like portion in theimages obtained at the plurality of positions of the illumination. 10.The method as set forth in claim 6, wherein the obtaining includesobtaining the one of the plurality of regions at a position 90 degreesrotated away from the notch when the uppermost substrate is circular.11. The method as set forth in claim 6, wherein the obtaining includesobtaining the one of the plurality of regions at a position 180 degreesrotated away from the notch when the uppermost substrate is circular.12. The method as set forth in claim 2, wherein the obtaining includesusing a tilted lens optic.
 13. The method as set forth in claim 1,wherein the applying includes forming a plane by incident light andreflected light of the illumination that intersects a radial directionof the uppermost substrate, when the uppermost substrate is circular.14. The method as set forth in claim 1, wherein the applying includespatterning the illumination to extend in a radial direction of theuppermost substrate, when the uppermost substrate is circular.
 15. Themethod as set forth in claim 14, wherein the applying includes scanningthe illumination in a direction intersecting the radial direction, theobtaining includes obtaining images of the region at a plurality ofpositions of the illumination created by the scanning of theillumination, and the identifying the position of the uppermostsubstrate includes identifying a position of a characteristic includedin the edge based on the position of the step-like portion in the imagesobtained at the plurality of positions of the illumination.
 16. Anapparatus comprising: an illuminating section that applies illuminationto a region covering a portion of an edge of an uppermost substrate anda portion of a lower substrate stacked with the uppermost substrate; anda position identifying section that identifies a position of the edge ofthe uppermost substrate based on a position of a step-like portionpresent in the region due to a step formed between the uppermostsubstrate and the lower substrate; wherein at least one of theapplication of illumination and the position identification is performedat an obliquely downward angle with respect to a plane orientation ofthe lower substrate.
 17. The apparatus as set forth in claim 16, furthercomprising an image obtaining section that obtains at least one of anupper reflection image formed by reflection from the uppermost substrateand a lower reflection image formed by reflection from the lowersubstrate, wherein the position identifying section identifies thestep-like portion based on one of the upper reflection image and thelower reflection image.
 18. The apparatus as set forth in claim 17,wherein the position identifying section detects the step-like portionbased on a difference in luminance between the upper reflection imageand the lower reflection image.
 19. The apparatus as set forth in claim17, further comprising a plurality of the illuminating sections operableto apply illumination to a plurality of regions of the uppermostsubstrate; and a plurality of the image obtaining sections incorrespondence with the plurality of illuminating sections.
 20. Theapparatus as set forth in claim 16, wherein the illuminating sectionapplies the illumination in such a manner that a plane formed byincident light and reflected light of the illumination intersects aradial direction of the uppermost substrate, when the uppermostsubstrate is circular.